Void / Vacuum

Gases & Other

Density: 0 g/cm³

Vacuum or void region. No material is present; particles stream freely through these regions.

Composition

Nuclide / Element	Fraction

MCNP

c Void / Vacuum
c No material card needed.
c Use material number 0 on the cell card:
c   1  0  -1    $ void cell inside surface 1

In MCNP, void cells use material number 0 with no density. In Serpent, use the keyword "void". In OpenMC, leave Cell.fill as None.